Methods for treating premature ejaculation are presented. More particularly and in one aspect, methods for treating premature ejaculation by administration of a neurotoxin, such a botulinum neurotoxin, to a patient are provided.
Premature ejaculation (PE) is a common sexual dysfunction in men, particularly those in the age range of about 18 to about 40 years old. Premature ejaculation can be generally defined as the occurrence of ejaculation prior to or sooner than hoped for by one or both sexual partners [e.g. see ‘The Merck Manual’, 16th Edition, p 1576, published by Merck Research Laboratories, 1992]. As one example, premature ejaculation can be experienced as ejaculation before, upon or shortly after penile penetration of a sexual partner. If the instances of premature ejaculation are few and far between, then such occurrences may not be a cause for concern. However, if instances of premature ejaculation occur practically every time intercourse is attempted, or even if premature ejaculation occurs even greater than about 10% or about 20% of the time intercourse is attempted, then treatment of the condition is likely to be warranted.
Premature ejaculation may be classified as primary or secondary, in accordance with the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), which classifies sexual disorders into 4 particular categories: (1) primary, (2) general medical condition-related, (3) substance-induced, and (4) not otherwise specified. Primary applies to individuals who have had the condition since they became capable of functioning sexually (i.e., postpuberty). Secondary indicates that the condition manifests itself in an individual where an acceptable level of ejaculatory control was previously had, and then began to experiencing premature ejaculation thereafter. With secondary premature ejaculation, the problem does not relate to a general medical disorder, and it is usually not related to substance inducement, however, hyperexcitability might in particular instances relate to psychotropic drug use and resolves when the drug is withdrawn.
The prevalence rate of premature ejaculation in American males is estimated to range from 30-70%. The National Health and Social Life Survey (NHSLS) indicates a prevalence of 30%, which is fairly steady through all adult age categories. Premature ejaculation can occur at virtually any age in an adult man's life. As a reported condition, it is most common in younger men (aged 18-30 years old) but may also occur in conjunction with secondary impotence in men aged 45-65 years.
Compositions that can be utilized for treating premature ejaculation are known. For example, use of selective serotonin reuptake inhibitors (SSRI's) for treating premature ejaculation are known and claimed, for example, in U.S. Pat. No. 7,105,516 which is directed to novel SSRI's effective for the treatment of premature ejaculation, as well as U.S. Pat. No. 6,777,437. Additional methods for treating premature ejaculation can be found in U.S. Pat. No. 6,974,839, which teaches administration of an effective amount of a tramadol (a monoamine uptake inhibitor) material to a male prior to sexual intercourse, and in U.S. Pat. No. 6,495,154, which claims delaying the onset of ejaculation in a male by systemically administering to the individual a rapid-release pharmaceutical formulation containing clomipramine and pharmacologically acceptable acid addition salts thereof. U.S. Pat. No. 7,018,648 is directed to a transdermal device for administering testosterone and/or at least one derivative thereof to treat premature ejaculation; U.S. Pat. No. 6,593,335 is directed to method of treating premature ejaculation by administration of a potassium channel opener; U.S. Pat. No. 6,727,283 discloses oral ingestion of an essentially nonaqueous, liquid concentrate of sertraline hydrochloride. In some examples, fluoxetine or paroxetine, (20 mg and 40 mg, respectively, and taken daily) are also prescribed in order to treat premature ejaculation. Other approaches that are known include application of topical anesthetics, such as lidocaine 5% cream, for example, to the penis before intercourse. Drawbacks associated with the use such anesthetics include undesired reduction in sensitivity and/or short term inability of the patient to achieve an erection.
The anaerobic, gram positive bacterium Clostridium botulinum produces a potent polypeptide neurotoxin, botulinum neurotoxin, which causes a neuroparalytic illness in humans and animals referred to as botulism, however this neurotoxin has now been utilized for decades for treating various conditions in human beings. One unit (U) of botulinum toxin is defined as the LD50 upon intraperitoneal injection into female Swiss Webster mice weighing 18-20 grams each. In other words, one unit of botulinum toxin is the amount of botulinum toxin that kills 50% of a group of female Swiss Webster mice. Seven generally immunologically distinct botulinum neurotoxins have been characterized, these being respectively botulinum neurotoxin serotypes A, B, C1, D, E, F, and G, each of which is distinguished by neutralization with type-specific antibodies. The different serotypes of botulinum toxin vary in the animal species that they affect and in the severity and duration of the paralysis they evoke. For example, it has been determined that botulinum toxin type A is 500 times more potent, as measured by the rate of paralysis produced in the rat, than is botulinum toxin type B. Additionally, botulinum toxin type B has been determined to be non-toxic in primates at a dose of 480 U/kg which is about 12 times the primate LD50 for botulinum toxin type A. The botulinum toxins apparently bind with high affinity to cholinergic motor neurons, are translocated into the neuron and block the presynaptic release of acetylcholine.
Botulinum toxins have been used in clinical settings for the treatment of neuromuscular disorders characterized by hyperactive skeletal muscles. Botulinum toxin type A was approved by the U.S. Food and Drug Administration in 1989 for the treatment of essential blepharospasm, strabismus and hemifacial spasm in patients over the age of twelve. In 2000 the FDA approved commercial preparations of type A and type B botulinum toxin serotypes for the treatment of cervical dystonia, and in 2002 the FDA approved a type A botulinum toxin for the cosmetic treatment of certain hyperkinetic (glabellar) facial wrinkles. Clinical effects of peripheral intramuscular botulinum toxin type A are usually seen within one week of injection and sometimes within a few hours. The typical duration of flaccid muscle paralysis from a single intramuscular injection of botulinum toxin type A can be about three months, although in some cases the effects of a botulinum toxin induced denervation of a gland, such as a salivary gland, have been reported to last for several years.
Although all the botulinum toxins serotypes apparently inhibit release of the neurotransmitter acetylcholine at the neuromuscular junction, they do so by affecting different neurosecretory proteins and/or cleaving these proteins at different sites. Botulinum toxin A is a zinc endopeptidase which can specifically hydrolyze a peptide linkage of the intracellular, vesicle associated protein SNAP-25. Botulinum type E also cleaves the 25 kiloDalton (kD) synaptosomal associated protein (SNAP-25), but targets different amino acid sequences within this protein, as compared to botulinum toxin type A. Botulinum toxin types B, D, F and G act on vesicle-associated protein (VAMP, also called synaptobrevin), with each serotype cleaving the protein at a different site. Finally, botulinum toxin type C1 has been shown to cleave both syntaxin and SNAP-25.
Regardless of serotype, the molecular mechanism of toxin intoxication appears to be similar and to involve at least three steps or stages. In the first step of the process, the toxin binds to the presynaptic membrane of the target neuron through a specific interaction between the heavy chain (H chain) and a cell surface receptor; the receptor is thought to be different for each serotype of botulinum toxin and for tetanus toxin. The carboxyl end segment of the H chain, HC, appears to be important for targeting of the toxin to the cell surface. In the second step, the toxin crosses the plasma membrane of the poisoned cell. The toxin is first engulfed by the cell through receptor-mediated endocytosis, and an endosome containing the toxin is formed. The toxin then escapes the endosome into the cytoplasm of the cell. This last step is thought to be mediated by the amino end segment of the H chain, HN, which triggers a conformational change of the toxin in response to a pH of about 5.5 or lower. Endosomes are known to possess a proton pump which decreases intra endosomal pH. The conformational shift exposes hydrophobic residues in the toxin, which permits the toxin to embed itself in the endosomal membrane. The toxin then translocates through the endosomal membrane into the cytosol. The last step of the mechanism of botulinum toxin activity appears to involve reduction of the disulfide bond joining the H and L chain. The entire toxic activity of botulinum and tetanus toxins is contained in the L chain of the holotoxin; the L chain is a zinc (Zn++) endopeptidase which selectively cleaves proteins essential for recognition and docking of neurotransmitter-containing vesicles with the cytoplasmic surface of the plasma membrane, and fusion of the vesicles with the plasma membrane. Tetanus neurotoxin, botulinum toxin B, D, F, and G cause degradation of synaptobrevin (also called vesicle-associated membrane protein (VAMP)), a synaptosomal membrane protein. Most of the VAMP present at the cytosolic surface of the synaptic vesicle is removed as a result of any one of these cleavage events. Each toxin specifically cleaves a different bond.
The molecular weight of the botulinum toxin protein molecule, for all seven of the known botulinum toxin serotypes, is about 150 kDa. Interestingly, the botulinum toxins are released by Clostridial bacterium as complexes comprising the 150 kD botulinum toxin protein molecule along with associated non-toxin proteins. Thus, the botulinum toxin type A complex can be produced by Clostridial bacterium as 900 kDa, 500 kDa and 300 kDa forms. Botulinum toxin types B and C1 are apparently produced as only a 500 kDa complex. Botulinum toxin type D is produced as both 300 kDa and 500 kDa complexes. Finally, botulinum toxin types E and F are produced as only approximately 300 kDa complexes. The complexes (i.e. molecular weight greater than about 150 kDa) are believed to contain a non-toxin hemagglutinin protein and a non-toxin and non-toxic nonhemagglutinin protein. These two non-toxin proteins (which along with the botulinum toxin molecule can comprise the relevant neurotoxin complex) may act to provide stability against denaturation to the botulinum toxin molecule and protection against digestive acids when toxin is ingested. Additionally, it is possible that the larger (greater than about 150 kDa molecular weight) botulinum toxin complexes may result in a slower rate of diffusion of the botulinum toxin away from a site of intramuscular injection of a botulinum toxin complex. The toxin complexes can be dissociated into toxin protein and hemagglutinin proteins by treating the complex with red blood cells at pH 7.3. The toxin protein has a marked instability upon removal of the hemagglutinin protein.
All the botulinum toxin serotypes are made by Clostridium botulinum bacteria as inactive single chain proteins which must be cleaved or nicked by proteases to become neuroactive. The bacterial strains that make botulinum toxin serotypes A and G possess endogenous proteases and serotypes A and G can therefore be recovered from bacterial cultures in predominantly their active form. In contrast, botulinum toxin serotypes C1, D, and E are synthesized by nonproteolytic strains and are therefore typically unactivated when recovered from culture. Serotypes B and F are produced by both proteolytic and nonproteolytic strains and therefore can be recovered in either the active or inactive form. However, even the proteolytic strains that produce, for example, the botulinum toxin type B serotype only cleave a portion of the toxin produced. The exact proportion of nicked to unnicked molecules depends on the length of incubation and the temperature of the culture. Therefore, a certain percentage of any preparation of, for example, the botulinum toxin type B toxin is likely to be inactive, possibly accounting for a lower potency of botulinum toxin type B as compared to botulinum toxin type A. The presence of inactive botulinum toxin molecules in a clinical preparation will contribute to the overall protein load of the preparation, which has been linked to increased antigenicity, without contributing to its clinical efficacy.
In vitro studies have indicated that botulinum toxin inhibits potassium cation induced release of both acetylcholine and norepinephrine from primary cell cultures of brainstem tissue. Additionally, it has been reported that botulinum toxin inhibits the evoked release of both glycine and glutamate in primary cultures of spinal cord neurons and that in brain synaptosome preparations botulinum toxin inhibits the release of each of the neurotransmitters acetylcholine, dopamine, norepinephrine, CGRP and glutamate.
High quality crystalline botulinum toxin type A can be produced from the Hall A strain of Clostridium botulinum with characteristics of ≧3×107 U/mg, an A260/A278 of less than 0.60 and a distinct pattern of banding on gel electrophoresis. The known Shantz process can be used to obtain crystalline botulinum toxin type A, as set forth in Shantz, E. J., et al, Properties and use of Botulinum toxin and Other Microbial Neurotoxins in Medicine, Microbiol Rev. 56: 80-99 (1992). Generally, the botulinum toxin type A complex can be isolated and purified from an anaerobic fermentation by cultivating Clostridium botulinum type A in a suitable medium. Raw toxin can be harvested by precipitation with sulfuric acid and concentrated by ultramicrofiltration. Purification can be carried out by dissolving the acid precipitate in calcium chloride. The toxin can then be precipitated with cold ethanol. The precipitate can be dissolved in sodium phosphate buffer and centrifuged. Upon drying there can then be obtained approximately 900 kDa crystalline botulinum toxin type A complex with a specific potency of 3×107 LD50 U/mg or greater. This known process can also be used, upon separation out of the non-toxin proteins, to obtain pure botulinum toxins, such as for example: purified botulinum toxin type A with an approximately 150 kDa molecular weight with a specific potency of 1-2×108 LD50 U/mg or greater; purified botulinum toxin type B with an approximately 156 kDa molecular weight with a specific potency of 1-2×108 LD50 U/mg or greater, and; purified botulinum toxin type F with an approximately 155 kDa molecular weight with a specific potency of 1-2×107 LD50 U/mg or greater.
Already prepared and purified botulinum toxins and toxin complexes suitable for preparing pharmaceutical formulations can be obtained from List Biological Laboratories, Inc., Campbell, Calif.; the Centre for Applied Microbiology and Research, Porton Down, U.K.; Wako (Osaka, Japan), as well as from Sigma Chemicals of St Louis, Mo.
It has been reported that a botulinum toxin has been used in clinical settings as follows:                (1) about 75-125 units of BOTOX® per intramuscular injection (multiple muscles) to treat cervical dystonia;        (2) 5-10 units of BOTOX® per intramuscular injection to treat glabellar lines (brow furrows) (5 units injected intramuscularly into the procerus muscle and 10 units injected intramuscularly into each corrugator supercilii muscle);        (3) about 30-80 units of BOTOX® to treat constipation by intrasphincter injection of the puborectalis muscle;        (4) about 1-5 units per muscle of intramuscularly injected BOTOX® to treat blepharospasm by injecting the lateral pre-tarsal orbicularis oculi muscle of the upper lid and the lateral pre-tarsal orbicularis oculi of the lower lid;        (5) to treat strabismus, extraocular muscles have been injected intramuscularly with between about 1-5 units of BOTOX®, the amount injected varying based upon both the size of the muscle to be injected and the extent of muscle paralysis desired (i.e. amount of diopter correction desired);        (6) to treat upper limb spasticity following stroke by intramuscular injections of BOTOX® into five different upper limb flexor muscles, as follows:                    (a) flexor digitorum profundus: 7.5 U to 30 U            (b) flexor digitorum sublimis: 7.5 U to 30 U            (c) flexor carpi ulnaris: 10 U to 40 U            (d) flexor carpi radialis: 15 U to 60 U            (e) biceps brachii: 50 U to 200 U. Each of the five indicated muscles has been injected at the same treatment session, so that the patient receives from 90 U to 360 U of upper limb flexor muscle BOTOX® by intramuscular injection at each treatment session;                        (7) to treat migraine, pericranial injected (injected symmetrically into glabellar, frontalis and temporalis muscles) injection of 25 U of BOTOX® has showed significant benefit as a prophylactic treatment of migraine compared to vehicle as measured by decreased measures of migraine frequency, maximal severity, associated vomiting and acute medication use over the three month period following the 25 U injection.        
Additionally, intramuscular botulinum toxin has been used in the treatment of tremor in patients with Parkinson's disease, although it has been reported that results have not been impressive. Marjama-Jyons, J., et al., Tremor—Predominant Parkinson's Disease, Drugs & Aging 16(4); 273-278:2000.
Treatment of certain gastrointestinal and smooth muscle disorders with a botulinum toxin are known. See e.g. U.S. Pat. Nos. 5,427,291 and 5,674,205 (Pasricha). Additionally, transurethral injection of a botulinum toxin into a bladder sphincter to treat a urination disorder is known (see e.g. Dykstra, D. D., et al, Treatment of detrusor-sphincter dyssynergia with botulinum A toxin: A double-blind study, Arch Phys Med Rehabil 1990 January; 71:24-6), as is injection of a botulinum toxin into the prostate to treat prostatic hyperplasia. See e.g. U.S. Pat. No. 6,365,164 (Schmidt).
U.S. Pat. No. 5,766,605 (Sanders) proposes the treatment of various autonomic disorders, such as hypersalivation and rhinitis, with a botulinum toxin.
Furthermore, various afflictions, such as hyperhidrosis and headache, treatable with a botulinum toxin are discussed in WO 95/17904 (PCT/US94/14717) (Aoki). EP 0 605 501 B1 (Graham) discusses treatment of cerebral palsy with a botulinum toxin and U.S. Pat. No. 6,063,768 (First) discusses treatment of neurogenic inflammation with a botulinum toxin. Erectile dysfunction has been reported as a symptom of botulism. Jenzer G., et al., Autonomic dysfunction in botulism B: a clinical report, Neurology 1975; 25:150-153; Naumann M. et al., Pure autonomic dysfunction in botulism type B, Naunyn Schmiedeberg's Archives of Pharmacology June 2002 (supp 2); 365 (abstract 89 at R31). This may be a result of circulating botulinum toxin present in a patient with botulism acting to block release of acetylcholine from cholinergic parasympathetic nerve endings in the corpora cavernosa of the penis. This would cause an inhibition of penile smooth muscle relaxation and therefore a reduced flow of blood into penile structures, and hence a flaccid penis. Contrarily, it has been speculated that a botulinum toxin can be used to cause an erection of the penis. Jones D. High performance. Nature 1989; 3:348.
It is known that botulinum toxin type A can have an efficacy for up to 12 months (European J Neurology 6 (Supp 4): S111-S1150:1999), and in some circumstances for as long as 27 months. The Laryngoscope 109:1344-1346:1999. However, the usual duration of an intramuscular injection of BOTOX® is typically about 3 to 4 months. The success of botulinum toxin type A to treat a variety of clinical conditions has led to interest in other botulinum toxin serotypes. Additionally, pure botulinum toxin has been used to treat humans. see e.g. Kohl A., et al., Comparison of the effect of botulinum toxin A BOTOX® with the highly-purified neurotoxin (NT 201) in the extensor digitorum brevis muscle test, Mov Disord 2000; 15(Suppl 3):165. Hence, a pharmaceutical composition can be prepared using a pure botulinum toxin.
The botulinum toxin molecule (about 150 kDa), as well as the botulinum toxin complexes (about 300-900 kDa), such as the toxin type A complex are also extremely susceptible to denaturation due to surface denaturation, heat, and alkaline conditions. Inactivated toxin forms toxoid proteins which may be immunogenic. The resulting antibodies can render a patient refractory to toxin injection. A commercially available botulinum toxin containing pharmaceutical composition is sold under the trademark BOTOX® (available from Allergan, Inc., of Irvine, Calif.). BOTOX® consists of a purified botulinum toxin type A complex, albumin, and sodium chloride packaged in sterile, vacuum-dried form. The botulinum toxin type A is made from a culture of the Hall strain of Clostridium botulinum grown in a medium containing N-Z amine and yeast extract. The botulinum toxin type A complex is purified from the culture solution by a series of acid precipitations to a crystalline complex consisting of the active high molecular weight toxin protein and an associated hemagglutinin protein. The crystalline complex is re-dissolved in a solution containing saline and albumin and sterile filtered (0.2 microns) prior to vacuum-drying. BOTOX® can be reconstituted with sterile, non-preserved saline prior to intramuscular injection. Each vial of BOTOX® contains about 100 units (U) of Clostridium botulinum toxin type A complex, 0.5 milligrams of human serum albumin and 0.9 milligrams of sodium chloride in a sterile, vacuum-dried form without a preservative.
To reconstitute vacuum-dried BOTOX® sterile normal saline without a preservative; 0.9% Sodium Chloride injection is used by drawing up the proper amount of diluent in the appropriate size syringe. Since BOTOX® is denatured by bubbling or similar violent agitation, the diluent is gently injected into the vial. BOTOX® should be administered within four hours after reconstitution. During this time period, reconstituted BOTOX® is stored in a refrigerator (2° to 8° C.). Reconstituted BOTOX® is clear, colorless and free of particulate matter. The vacuum-dried product is stored in a freezer at or below −5° C. BOTOX® is administered within four hours after the vial is removed from the freezer and reconstituted. During these four hours, reconstituted BOTOX® can be stored in a refrigerator (2° to 8° C.).
Other commercially available botulinum toxin containing pharmaceutical compositions include DYSPORT® (Clostridium botulinum type A toxin haemagglutinin complex with albumin and lactose in the formulation, available from Ipsen Limited, Berkshire, U.K. as a powder to be reconstituted with 0.9% sodium chloride before use), and MYOBLOC™ (an injectable solution comprising botulinum toxin type B, human serum albumin, sodium succinate, and sodium chloride at about pH 5.6, available from Solstice Neurosciences, Inc).
What is needed therefore is a simple method for treating premature ejaculation and/or prolongation of climax time. In particular, a long lasting, non-systemic method for treating premature ejaculation and/or prolongation of climax time is desired that does not entail oral or repeated ingestion of a pharmaceutical compound prior to engaging in sexual activity.